Last Updated May 26, 2021
As the COVID-19 pandemic has forced us to spend more time indoors, the air in our homes may have potentially become stale. This can occur if doors and/or windows have been kept closed for a prolonged amount of time, as well as the usage of ventilators and/or air conditioners whose filters may have not been cleaned.
This article aims to promote the importance of maintaining good indoor air quality and how you can do so by owning an air purifier. Continue reading to learn more!
Why Does Indoor Air Quality Matter?
According to the United States Environmental Protection Agency (EPA), indoor air quality refers to “the quality of the air in a home, school, office, or other building environment.”
Pollutants in the Air
As it has been found that Americans, on average, spend approximately 90 percent of their time indoors, it is important to maintain good indoor air quality as concentrations of some pollutants found in indoor air can reach up to 5 times higher than concentrations in outdoor air.
Typical pollutants and sources include:
- Organic compounds from a variety of products and materials;
- Ozone chemicals, typically from aerosols and air cleaners;
- Pesticides, lead and asbestos;
- Biological agents, such as molds;
- Other substances, such as radon and pet dander;
- Combustion byproducts, such as carbon monoxide, particulate matter and tobacco smoke.
1. Outdoor sources
Pollutants derived from outdoor sources can easily enter homes and other buildings through open doors and/or windows, ventilation systems, building foundations and even cracks or gaps in the structures. For example, one pollutant substance is radon, which naturally occurs from rocks or soil decay in the ground, which can enter buildings through cracks or gaps.
Volatile organic compounds (VOCs) could be chimney smoke or chemicals in water supplies, as well as soil, dust or dirt that cling to people’s clothing as they enter a house or building.
Other factors that can also affect indoor air quality are outdoor climate and weather conditions. For instance, a humid climate can accelerate mold growth due to increased potential for indoor moisture. Furthermore, weather conditions can influence home or building occupants to keep windows open or closed as well as whether or not to operate an air conditioner, humidifier or heater.
2. Indoor sources
These range from combustion sources to cleaning supplies to even building materials.
Combustion sources include tobacco smoke, burning wood and coal heating, whether it be from fireplaces or barbeque grills. These can release gases such as carbon monoxide, which can be lethal if they reach high concentrations in a small area of space, and/or nitrogen dioxide.
Cleaning supplies are not the only ones that can exude chemicals or pollutants in the air; other examples are paints, pesticides, varnishes, waxes, moth repellents, air fresheners and aerosol cans.
Building materials can be of those in a degrading state, such as asbestos fibers which can be released into the air from building insulation or in a new state, such as chemicals rising from pressed wood.
Effects on Human Health
Poor indoor air quality can have adverse health effects, which can range from minor to severe. According to the US EPA, the lungs are the most common site of injury by airborne pollutants, while common health effects include:
- Irritation of the eyes, nose and throat;
- Headaches, dizziness and/or fatigue;
- Respiratory disease, heart disease and/or cancer.
There is a clear established link between common airborne pollutants with health effects, such as radon being the second leading cause of lung cancer and various indoor air pollutants— dust mites, mold, pet dander, tobacco smoke and others– being ‘asthma triggers‘, meaning that asthmatics may experience asthma attacks upon being exposed to these pollutants.
Other indoor air quality issues are still being understood, meaning that there may be a link between these issues with people’s health; one example in particular is “sick building syndrome“. This occurs when the house or building occupants experience similar symptoms after entering the house or building, however, this symptoms diminish or disappear on their own after the occupants exit the house or building.
What Does an Air Purifier Do?
According to the US EPA, air purifiers, also known as portable air cleaners or air sanitizers, are “designed to filter the air in a single room or area“. It is an effective way to improve indoor air to reduce or remove the sources of pollutants and to ventilate with clean outdoor air.
In addition, research shows that filtration via air purifiers can be an effective supplement to source control and ventilation. Although an air purifier can reduce indoor air pollution, they may not always be able to remove all pollutants in the air.
How Does an Air Purifier Work?
Generally, an air purifier would have a filter, or multiple filters, and a fan which sucks in, circulates then exhausts the air. When the fan does suck in air, it moves through the filter, which captures pollutants and particles. Therefore, the air that is exhausted, or pushed back out, is ‘purified’ air.
Parameter Used for Efficiency in Pollutant Removal
According to the US EPA, understanding the fractional removal efficiency of pollutants an air purifier is designed to remove enables us to assess which units are more efficient or effective in removing pollutants. A commonly used test in measuring this in the United States is the ASHRAE Standard 52.2, which “evaluates the removal efficiency for particles 0.3 to 10 μm in diameter. Results are reported as a Minimum Efficiency Reporting Value (MERV) ranging from MERV 1 to MERV 16 based on the average removal efficiency across
three particle size ranges: 0.3–1 μm, 1–3 μm and 3–10 μm.”
Types of Filters in Air Purifiers
Filters are typically made of paper, fiber or fiberglass, or mesh.
Most filters have been designed to capture particles, but not gases like volatile organic compounds (VOCs) or radon— an adsorbent, like activated carbon, would be more suited for this.
1. HEPA Filter
One filter in particular is called the HEPA filter. HEPA itself is short for High Efficiency Particulate Air and it is a type of filter which captures particles of various sizes within a multi-layered netting usually made out of fine fiberglass threads. In other words, it is a type of pleated filter. As a result, the filter is comprised of a dense sheet of pleated small fibers sealed within a metal or plastic frame, making it extremely airtight.
This type of filter is constructed with a weave looser than the HEPA filter. Due to it being not as airtight, it is only capable of trapping large particles. In a way, this supports HEPA filters from becoming prematurely ‘clogged’ with pollutants.
3. Electrostatic Air Filter
This unique filter uses an electrically charged panel, or screen, to capture particles. An ionizer, also known as an ion-generating air cleanser, operates by attaching electrically charged ions to dust, dander and other particles or pollutants, which causes them to be heavier and drop from the air.
4. Fibrous Media Air Filter
These remove particles by capturing them onto fibrous filter materials, hence its name.
According to the US EPA, the efficiency of this process “depends on a number of parameters including particle size, face velocity, filter thickness, filter porosity, filter fiber dimensions, dust loading conditions, and whether or not the media are modified by the manufacturer to initially have an electrostatic charge on the fibers (e.g., electret vs. non-electret media).”
5. Activated Carbon Filter
As mentioned before, these type of filters are uniquely designed to help trap odor and gases from the air, thanks to its activated carbon material. However, it should be noted that this type of filter is not commonly used for home air purifiers.
6. Sorbent Media Air Filter
This type of filter uses a material that has a very high surface area called a sorbent, which captures gaseous pollutants. There are two common sorbent processes which remove gaseous pollutants: adsorption and chemisorption. As explained by the US EPA:
Adsorption is a physical process in which gas or vapor molecules become attracted to a surface. What happens is that the adsorbent will absorb molecules for which it has the greatest affinity.
Chemisorption is a chemical process in which gas or vapor molecules have a chemical reaction with sorbent material or other reactive agents that have been embedded within the sorbent. Upon this reaction, the material, or reactive agents, form stable chemical compounds that are “bound to the media as organic or inorganic salts, or are broken down and released into the air as carbon dioxide, water vapor, or some material more readily adsorbed by other adsorbents.”
How Many Air Purifiers Should You Have?
Given that each consumer’s home varies in size and the number of rooms it holds, it is reasonable for one to wonder how many air purifiers they should have to ensure that clean air is maintained throughout the entire household.
This depends on two factors.
1. Square footage of your home. This correlates to the amount of air that will need to be purified.
For instance, if you live in a house that is bigger than 500 sq ft, it is likely that you will need more than one air purifier in order to properly clean the air in each room.
2. The capacity of the air purifier. This correlates to how much air a single air purifier unit is capable of purifying.
The volume of indoor air alone can be calculated as well. An equation derived by Learn Metrics suggests: Volume (indoor air) = Indoor area (in sq ft) x Ceiling height (in ft). Using this equation, assuming you live in a 1,000 sq ft home with 8 ft ceiling height, the total volume of indoor air would be 8,000 cubic feet.
If the air needs to be cleaned 4 times every hour, then that would equal to 32,000 cubic feet of air that needs to be cleaned per hour. An air purifier commonly has an airflow of 200 cubic feet of air per minute, or 12,000 cubic feet per hour. In this scenario, at least three air purifiers will be needed.
If you are still uncertain how many air purifiers you need based on the coverage area, you can access a helpful guide provided by Learn Metrics.
Silent Air Purifier – Why Does Quiet Matter?
Having fresh indoor clean air is great– it improves your health, can help you concentrate better and feel well energized. But what would the use be if you obtained it at the expense of you or your family’s comfort?
Everyone has their own level of tolerance and preference for noise. However, having an air purifier around the house that creates too much noise disturbance could affect your ability to focus or rest optimally. This is why quiet matters.
Do Silent Air Purifiers Work Just as Well as Regular Air Purifiers?
Yes. The noise from an air purifier is typically considered ambient noise. However, the volume of noise varies depending on the model and operating speed of the air purifier. Essentially, they function more or less the same as regular air purifiers.
However, certain factors may need to be accounted for when considering the noise emitted by air purifiers, including ‘silent’ ones:
- A quiet or ‘silent’ air purifier will emit more sound at higher speeds. In other words, the harder it works, the more noise it makes.
- The level of noise generated by the air purifier can be influenced by the nature of the room it is placed in. Carpeted, well-furnished or thick-walled rooms are more capable of absorbing noise.
- The air purifier industry does not have any standards for sound emissions. There are no existing industry regulations which mandate air purifier manufacturers to disclose the level of noise its products generates, which can affect consumer expectations– a ‘silent’ air purifier may be deemed noisy, depending on the consumer’s own noise tolerance.
How Noise Levels of Air Purifiers are Measured
Decibels (dB) * A
Like all other sound-emitting objects, a ‘silent’ air purifier’s sound/noise levels can be measured in decibels (dB), and is typically multiplied with an ‘A’ factor, which is basically the effect onto a human upon hearing the sound/noise. In short, when you are reviewing air purifiers to purchase, select those with the lowest dB(A) in its product specifications.
It is to be noted that the dB(A) scale goes up in powers of ten, due to it being logarithmic and based on mathematics and practicality. Therefore, when you are comparing between an air purifier that is marked as 70 db(A) against one that is 60 dB(A), this means that the former is ten times noisier than the latter.
Sound Pressure and Sound Power are Not the Same
However, it is important to also be aware on the concept of sound pressure vs sound power. Both are measured in db(A), which can make it confusing.
Sound pressure is where there is an actual change in air pressure due to there being a vibrating source. A normal conversation could be at a sound pressure of 60 dB(A), but its sound power is 70 dB(A).
Due to this, it is good to be wary of manufacturers that might label their air purifiers based on sound pressure, to make it appear lower and, therefore, give the impression that its product is not as noisy, when in reality its sound power is higher. Therefore, when comparing air purifiers, it is important to assess if the manufacturer is labelling its air purifier based on sound pressure or sound power.
Measured based on sound pressure, a very quiet air purifier should be around 20 dB(A), while a good air purifier on its low setting would usually be 32 dB(A). However, a typical air purifier on its low setting could be around 36 dB(A).
How to Choose the Best Air Purifier
When selecting an air purifier, US EPA emphasizes that it is important to keep the following in mind:
- No air purifier, cleaner or filter will eliminate all of the air pollutants in your house.
Most purifiers can only filter either particles or gases, however in order for them to filter both particles and gases, then the purifier will contain two filters– one for particles and another for gases.
- All filters need regular replacement.
The air purification process will not be as effective if its filter is dirty and overloaded.
- Choose one that has a clean air delivery rate (CADR) that is large enough for the size of the room or area it will be operated in.
This is because the greater the CADR, the more particles that can be filtered and the larger the area it can operate in. It should be noted that the CADR rating system is for particles only. (Note: CADR is a metric developed by the Association of Home Appliance Manufacturers (AHAM) which helps consumers understand how effective a device is at filtering various particles in a specific room size.)
- Choose one with an activated carbon filter or other filters suited for removing gases if you aim to filter gases, particularly ones with odor.
An air purifier with a high CADR and activated carbon filter would be capable of filtering both particles and gases.
- Higher fan speeds and longer run times will increase the amount of air filtered.
Typically filtration is greater at higher fan speeds, so having the purifier operate for a longer time at high fan speeds can increase air filtration and, therefore, improve indoor air quality.
- Consider one that is ENERGY STAR® certified.
This means that the product meets strict energy efficiency guidelines set by US EPA and the US Department of Energy.
How to Take Care of Your Air Purifier
Purchasing an air purifier is quite an investment— a lifetime one, some may say.
This is because there is a high upfront cost of purchasing the hardware, then a periodic cost of purchasing filters to replace the used ones; not to mention the impact onto your monthly electricity bill. Filter replacement costs vary by product and brand– there are expensive ones which can last for years and there are those that are cheap but need frequent replacement. Some are even washable, while others are disposable only.
Filter Replacement/Cleaning or Plate Cleaning
As mentioned above, you will need to routinely replace or clean your air purifier’s filter. This is because after days or weeks of use, the filter is bound to become filled and lined up with all the pollutants that it has caught in its seams. Continuing to use the air purifier whilst its filter is already heavily ‘clogged’ will render the machine ineffective as it can no longer properly clean the air.
Pre-filters can either be washed or replaced, depending on the model purchased; HEPA filters and activated carbon filters need to be replaced.
However, the replacement of filters is not applicable to electrostatic air cleaners. For this model type, it is actually quite easy and inexpensive to maintain. This is because these units only require that you regularly wash its plates, generally once a week.
The US EPA highlights that “caution should be exercised during replacement and cleaning of filter media and other air cleaner components.” This means that efforts should be made to prevent pollutants are not re-emitted into the air and also do not come into contact with the user’s skin. Efforts include minimizing excessive movement; avoiding air drafts when filters are removed; and wearing mask and gloves.
Keeping Surroundings Clean
It is important to keep the area around the air purifier clean. This is because having accumulated dirt, like dust bunnies, adds unnecessary work for the air purifier, which could potentially make it consume even more electricity than necessary.
Place it in a Spacious Area
Ideally speaking, placing the unit in a room with closed doors and windows may be best, as this keeps contaminated air from entering the room. Outdoor air may contain even more pollutants, which would not take long for the air purifier’s filters to quickly become ‘clogged’. Furthermore, a unit can function more effectively if it has adequate space all around it to enable proper air intake and release.
Dust buildups can occur over time, which can fill up the exterior grills and/or panels of the air purifier. It would be beneficial to clean them with a cloth, vacuum it, or in accordance with the manufacturer’s cleaning instructions.
Should an Air Purifier be Kept on All Day?
Yes. It would be ideal to do so, as it is not possible for the room to remain clean with only a couple of hours of runtime. By having the machine on and running, it can continuously draw air through its filters and, thus, clean it. Once it has been turned off, it will stop filtering the air and potentially harmful particles or pollutants will gradually return within two to four hours since it had been switched off.
You can sleep with it on as well, so that it continues to capture any pollutants, such as dust mites, mold, dander and bacteria, while you rest.
The quality of air is influenced by the levels of pollutants in it– the more pollutants exhausted from various sources, the lower the quality of air will be. Maintaining good indoor air quality is highly important for our health, especially as we cope with the COVID-19 pandemic. With clean air, not only are we at lower risk of negative physical health effects but also of negative mental effects, such as impact on concentration and emotions. Therefore, air purifiers can play a significant role, as they are uniquely designed for cleaning the air we breathe. They function with the help of a fan and filters, which can either be washable or disposable, depending on the model. Silent air purifiers are essentially the same as regular air purifiers, except that they operate at a lower sound pressure level. When selecting an air purifier, especially if you are opting for the silent version, it is important that you check if there is any disclosure on the noise level the product emits, and whether it is measured in sound pressure or sound power, as well as that its CADR is large enough for the room or area the unit will be operating in.
- “Indoor Air Quality,” United States Environmental Protection Agency, https://www.epa.gov/report-environment/indoor-air-quality
- “Care for Your Air: A Guide to Indoor Air Quality,” United States Environmental Protection Agency, https://www.epa.gov/indoor-air-quality-iaq/care-your-air-guide-indoor-air-quality
- “Guide to Air Cleaners in the Home 2nd Edition,” 2018, United States Environmental Protection Agency, https://www.epa.gov/sites/production/files/2018-07/documents/guide_to_air_cleaners_in_the_home_2nd_edition.pdf
- “Do Air Purifiers Actually Work?,” 2020, Good Housekeeping, https://www.goodhousekeeping.com/appliances/air-purifier-reviews/a25252001/do-air-purifiers-work/
- “How Many Air Purifiers Do I Need? One For Every Room?,” 2020, LearnMetrics, https://learnmetrics.com/how-many-air-purifiers-do-i-need/
- “Sleep your best sleep with a quiet air purifier,” 2020, Blueair, https://www.blueair.com/id/quiet-air-purifier.html
- “ARE AIR PURIFIERS LOUD?,” 2020, HVAC.com, https://www.hvac.com/faq/air-purifiers-loud/#:~:text=An%20air%20purifier%27s%20noise%20level,up%20in%20powers%20of%20ten.
- “How to assess an air purifier’s noise levels?,” 2014, Allergy Cosmos, https://www.allergycosmos.co.uk/blog/how-to-assess-an-air-purifiers-noise-levels/
- “Should You Buy an Air Purifier?,” 2019, The Spruce, https://www.thespruce.com/should-you-buy-an-air-purifier-1708890
- “Buying an air purifier? Here’s what you need to know,” 2020, Tom’s Guide, https://www.tomsguide.com/reference/air-purifier-buying-guide
- “Air Purifier Maintenance,” Sylvane, https://www.sylvane.com/air-purifier-maintenance.html
- “CAN YOU LEAVE AIR PURIFIER ON ALL THE TIME,” 2020, AirFuji.com, https://airfuji.com/can-you-leave-air-purifier-on-all-the-time/
- “Air Purifier Maintenance Guide,” AchooAllergy.com, https://www.achooallergy.com/blog/learning/air-purifier-maintenance-guide/
- “Residential Air Cleaners: A Technical Summary,” 2018, United States Environmental Protection Agency, https://www.epa.gov/sites/production/files/2018-07/documents/residential_air_cleaners_-_a_technical_summary_3rd_edition.pdf